Many of today's handheld devices make use of wireless “connections” for telephony, digital data transfer, geographical positioning, and the like. Despite differences in frequency spectra, modulation methods, and spectral power densities, the wireless connectivity standards use synchronized data packets to transmit and receive data. In general, all of these wireless capabilities are defined by industry-approved standards (e.g. IEEE 802.11 and 3GPP LTE) which specify the parameters and limits to which devices having those capabilities must adhere.
At any point along the device-development continuum, it may be necessary to test and verify that a device is operating within its standards' specifications. Most such devices are transceivers, that is, they transmit and receive wireless RF signals. Specialized systems designed for testing such devices typically contain subsystems designed to receive and analyze device-transmitted signals (e.g., vector signal analyzers or VSAs) and to send signals (e.g., vector signal generators or VSGs) that subscribe to the industry-approved standards so as to determine whether a device is receiving and processing the wireless signals in accordance with its standard.
In testing wireless devices that employ multiple input/multiple output (MIMO) technology, the most accurate testing will simulate real-world environments. Thus, if a MIMO device has two antennas, two transmitters and two receivers (e.g., a 2×2 MIMO device), the most accurate testing would involve doing receive signal (RX) testing using two VSGs and transmit signal (TX) testing using two VSAs, plus some means of synchronizing the VSA and VSG operations.
When such single VSA/VSG testers are used to test TX functions of a device under test (DUT), the TX signals are sampled one at a time by the VSA using a multiplexing or switching scheme. Thus, one is unable to fully simulate the environment where multiple TX signals are transmitted simultaneously.
One can, in fact, simulate real-world environments using testers equipped with multiple VSAs and VSGs, and synchronization. And, it could be possible to build up such a test capability by using two or more single VSA/VSG testers to create a N×N MIMO test capability (where N≧2). However, the concatenation of such testers is not trivial. There are triggering issues that must be resolved in order to have the combination simulate real-world MIMO conditions. For example, each tester must have the ability to trigger the others as the DUT may not use all transmitters it has available.
Therefore, a system and method designed to support routine concatenation of single VSA/VSG test systems which provides an expandable triggering capability would provide a faster, simpler means for combining such testers while offering more accurate simulation of real-world MIMO environments and conditions. Furthermore, since MIMO is not limited to 4×4, having dedicated trigger lines for each tester is less desirable than have a scalable solution that permits one to add new testers as the N-level of N×N MIMO increases.